Field of the Invention
The invention relates to methods and materials useful in organic semiconductor devices.
Related Art
A new generation of electronic devices including field-effect transistors and photovoltaic cells as organic photovoltaics (OPVs) and organic light-emitting transistors (OLETs) is being fabricated using organic semiconductors as their active components. Conjugated polymer are useful in these devices as they combine the electrical properties of semiconductors with the mechanical properties of plastics. Moreover, these materials can be processed inexpensively by techniques such as spin-coating and ink-jet printing. For this reason, they are finding applications in optoelectronic devices such as plastic light-emitting diodes (LEDs) and photovoltaic cells. Because conjugated polymers can be designed to form active layers in these types of electronic devices, these polymers provide promising materials for optimizing the performance of existing devices as well as the development of new devices.
Field-effect transistors (FETs) fabricated from conjugated polymers are candidates for use in flexible, transparent, and low-cost electronic applications, such as electronic paper or organic light-emitting diode displays (see, e.g. Allard et al., Angew. Chem. Int. Ed. 47, 4070-4098 (2008)). In addition to the advantage of cost-effect production from solution processing, polymer based FETs also have the potential for excellent charge transport characteristics. During the past decade, improvements in conjugated polymer design and device fabrication have resulted in the achievement of field-effect mobilities close to that of amorphous silicon (0.1˜1 cm2/Vs).
Organic field-effect transistors (OFETs) are of particular interest because of the continuing improvements of the charge carrier mobility that are promising for use in “plastic electronics” with unique properties like flexibility, transparence, and low cost. Significant progress has been made in solution-processed OFETs based on small molecules and polymer semiconductors (≈10 cm2/Vs), which make such devices closer to the industrial application (see, e.g. Diao et al., Nat. Mater. 2013, 12, (7), 7; Minemawari et al., Nature 2011, 475, (7356); and Li et al., Sci. Rep. 2012, 2, 9). The advantage of OFETs for applications focuses on low-cost with high throughput printing processes for mass production (see, e.g., Guo et al., Adv. Mater. 2010, 22, (40), 4427-4447; Arias et al., Chem. Rev. 2010, 110, (1), 3-24; and Sirringhaus, H. Adv. Mater. 2005, 17, (20), 2411-2425). Polymer semiconductors offer better potential for excellent charge transport as well as better film forming and mechanical properties compared with their small molecular counterpart (McCulloch et al., Nat. Mater. 2006, 5, (4); and Yan et al., Nature 2009, 457, (7230)).
Several strategies including process optimization and molecular design have been proposed to achieve long-range order of the polymer fibers and better polymer packing (see, e.g. Sirringhaus et al., Appl. Phys. Lett. 2000, 77, (3), 406-408; Pisula et al., Adv. Mater. 2005, 17, (6), 684-689; Duffy et al., Chem. Mater. 2008, 20, (23), 7252-7259; DeLongchamp et al., Acs Nano 2009, 3, (4), 780-787; Li et al., J. Am. Chem. Soc. 2010, 132, (26), 8807-8809; Ying et al., J. Am. Chem. Soc. 2011, 133, (46), 18538-18541; Tsao et al., J. Am. Chem. Soc. 2011, 133, (8), 2605-2612; and Kim et al., J. Nat. Mater. 2013, 12, (7), 6.). Art in this technology teaches that carrier mobility is strongly related to the MW, i.e. higher MW offers better mobility, mainly due to smooth polymer packing and less grain boundaries (see e.g., Tsao et al., J. Am. Chem. Soc. 2011, 133, (8), 2605-2612; Brinkmann et al., Macromolecules 2009, 42, (4), 1125-1130; Kline et al., Macromolecules 2005, 38, (8), 3312-3319; and Kline et al., J. Adv. Mater. 2003, 15, (18), 1519-1522). Low MW materials on the contrary have the trend to form crystalline fiber domains; however the grain boundaries strongly reduce the carrier mobility (see e.g. Jimison et al., Adv. Mater. 2009, 21, (16), 1568-1572; and Rivnay et al., Nat. Mater. 2009, 8, (12), 7). However, high MW materials can present difficulties during the fabrication process, such as difficulty to be dissolved and the high viscosity challenge for high-resolution inkjet printing process.
While the technology has advanced considerably in recent years, there is a continuing need in the art for materials and methods that allow artisans to form conjugated polymer compositions having new and improved functional properties, and in particular, those having improved charge mobilities.